Conventionally, in a process of manufacturing a semiconductor device and the like, an insulating layer (e.g., a CVD oxide film and the like) and the like are successively laminated on a silicon layer, e.g., a polysilicon layer forming an electrode, and then, the polysilicon layer and the CVD oxide film and the like formed thereon are patterned after a specific shape by an etching process and the like by using a photolithographic process. Thereafter, an oxide film is formed on exposed sidewalls and the like of the polysilicon layer by a thermal oxidation.
However, there has been a problem of the so-call “bird's beak formation”, in the process of manufacturing a semiconductor device in which the thermal oxidation continues to proceed into both end portions of the polysilicon layer at an interface portion between the polysilicon layer and the CVD oxide film or the like.
Since the bird's beak locally forms a thick oxide film without being controlled and the amount of oxidation varies, there generate adverse effects of a deterioration, a variation and the like on a performance of the semiconductor device.
Further, there has been proposed a technique to solve the problem, wherein a polysilicon layer, a CVD oxide film or the like are successively formed, and then, a nitride layer is formed on a surface portion of the oxide film and at an interface portion between the polysilicon layer and the CVD oxide film by a heat treatment in ammonia gas atmosphere. (see, Patent Reference 1)
However, the heat treatment is performed at a high temperature of, e.g., 700° C., and thus, an end portion of the interface between the polysilicon layer and the oxide film is oxidized to thereby become thick. Thus, since the entire manufacturing process of the next generation semiconductor device can be affected by the heat generated, it is hard to control a uniformly ultra-thin nitride layer in a fine accuracy. Therefore, this method cannot be favorably employed to improve and stabilize the performance of the semiconductor device.
As described above, conventionally, there has been the problem, the bird's beak, occurring at the interface portion between the polysilicon layer and the CVD oxide film or the like, and it is required to employ a high temperature heat treatment at to solve the problem. Consequently, there has been an increasing demand for developing a semiconductor device and a method for the manufacture thereof capable of providing uniformly ultra-thin nitrided region by suppressing the bird's beak through the use of a process performed at a lower temperature. Patent Reference 1: Japanese Patent Laid-open Application No. H10-335500